1. Field of the Invention
This invention relates to a thin film magnetic head of a magneto-resistance effect type.
2. Description of the Prior Art
A magnetic head of the magneto-resistance effect type is employed for various magnetic heads, for example, as a reproducing magnetic head of a magnetic recording and reproducing head assembly of a hard disk drive unit due to its superiority in high sensitivity in short wavelength. It is advantageous for a magneto-resistance effect type thin film magnetic head to adopt a shield type construction in order to assure a high resolution. A magneto-resistance effect type reproducing thin film magnetic head having such shield type construction can be made as a composite thin film magnetic head wherein it is formed as a unitary member together with a magnetic head of the inductive type acting as a recording magnetic head.
An exemplary one of conventional magneto-resistance effect type thin film magnetic head of such composite type is shown in FIGS. 9, 10 and 11 and 12 wherein such magnetic head is constructed as a floating type magnetic head. Referring to FIGS. 9 to 11, the magnetic head shown includes a base member 1 formed either from a slider which is caused to float by an air flow produced in response to rotation of a magnetic record medium such as, for example, a hard disk or from a base plate mounted on such slider. A lower layer thin film magnetic core 3 and an upper layer thin film magnetic core 4 are formed in an overlapping relationship on the base member 1 such that front ends thereof define therebetween a magnetic gap g opened to an opposing face of the magnetic head at which the magnetic head is contacted with or opposed to the magnetic record medium, that is, an air bearing surface 2 or the floating magnetic head. A magneto-resistance effect magnetic sensing section 5 is disposed in the magnetic gap g between the lower layer thin film magnetic core 3 and upper layer thin film magnetic core 4 and includes a magneto-resistance effect thin film which extends rearwardly from the magnetic gap g. A pair of electrodes 15a and 15b are formed at front and rear ends of the magneto-resistance effect magnetic sensing section 5.
A biasing conductor 7 in the form of a thin film conductive layer is formed between the lower and upper layer thin film magnetic cores 3 and 4 perpendicularly across the magneto-resistance effect magnetic sensing section 5 with a pair of insulator layers 6 interposed between the biasing conductor 7 and the lower layer thin film magnetic core 3 and between the biasing conductor 7 and the upper layer thin film magnetic core 4. The upper layer thin film magnetic core 4 is magnetically coupled at a rear end thereof to the lower layer thin film magnetic core 3, for example, through a window formed in the insulating layers 6 such that a closed magnetic path including the magnetic gap g therein is formed by the lower and upper layer thin film magnetic cores 3 and 4.
A head winding 8 in the form of a thin film conductive layer is formed, for example, on the lower layer thin film magnetic core 3 with another insulating layer 6 interposed therebetween, for example, in a spiral pattern such that it may surround the rear ends of the upper and lower layer thin film magnetic cores 4 and 3 at which the upper and lower thin film magnetic cores 4 and 3 are magnetically coupled to each other. The head winding 8 may be formed, for example, simultaneously with formation of the biasing conductor 7.
According to such thin film magnetic head, a magneto-resistance effect type magnetic head of the shield type is constructed such that the magneto-resistance effect magnetic sensing section 5 is disposed in the magnetic gap g defined between the front ends of the lower and upper layer thin film magnetic cores 3 and 4 in a condition wherein it is opened to a face, for example, the air bearing surface 2, of the magnetic head which is to contact with or is opposed to the magnetic record medium such that the magnetic cores 3 and 4 are constructed as magnetic shielding members. Thus, a signal magnetic field recorded on the magnetic record medium is applied to the magneto-resistance effect magnetic sensing section 5 by way of the magnetic gap g. In the meantime, a sensing current is flowed between the electrodes 15a and 15b through the magneto-resistance effect magnetic sensing section 5 while a required current is supplied to the biasing conductor 7. A magnetic field is thus produced by the biasing conductor 7 and applied to the magneto-resistance effect magnetic sensing section 5. Consequently, the magneto-resistance characteristic region of the magneto-resistance effect magnetic sensing section 5 which indicates a high sensitivity in a required magnetized condition and indicates a linearity is rendered operative. Thus, a variation in magnetic reluctance caused by a signal magnetic field provided from the magnetic record medium through the magnetic gap g as described is detected as a variation in voltage between the electrodes 15a and 15b.
On the other hand, upon recording upon the magnetic record medium, supply of a current to the biasing conductor 7 is stopped, and also supply of the sensing current i.sub.5 to the magneto-resistance effect magnetic sensing section 5 is stopped while a required current is now supplied to the head winding 8 in accordance with recording information. Consequently, a magnetic field produced in the closed magnetic path by the lower and upper layer thin film magnetic cores 3 and 4 is extracted from the magnetic gap g to effect magnetic recording upon the magnetic record medium. Thus, the magneto-resistance effect type thin film magnetic head is constructed as a composite magnetic head of a magneto-resistance effect type reproducing magnetic head and an inductive type recording magnetic head.
The composite magnetic head of a magneto-resistance effect type thin film magneto head with an inductive type recording magnetic head is manufacture in the following manner. Referring to FIGS. 12 to 14 in which the magnetic head is shown at a step in manufacturing the same, when such composite magnetic head of the magneto-resistance effect type is to be manufactured, a magnetic alloy such as, for example, FeNi is first plated, for example, by well known frame plating on a base member 1 under the application of a magnetic field, and then the frame which is made of a photo-resist or the like is removed and also the magnetic alloy at an unnecessary portion outside the region of the thus removed frame is removed by etching to form a lower layer thin film magnetic core 3.
The lower layer thin film magnetic core 3 is normally formed with a sufficiently great area comparing with a track width W.sub.T of a magnetic gap g to be finally obtained, that is, such a great area that it finally includes an entire region of a pattern of an upper layer thin film magnetic core 4. Then, a non-magnetic insulating layer 6 to SiO.sub.2, Al.sub.2 O.sub.3 or the like is formed by sputtering or by some other well known method over an entire region of the lower layer thin film magnetic core 3 formed in a required pattern of a wide area in this manner, and a surface of the insulating layer 6 is flattened. After then, such a magneto-resistance effect magnetic sensing section 5, a pair of electrodes 15a and 15b and so forth as described hereinabove are formed on the thus flattened surface of the insulating layer 6, and a biasing conductor 7, a head winding 8 and so forth are formed on them with an insulator layer 6 interposed therebetween. Further, an upper layer thin film magnetic core 4 is formed on them with another insulator layer 6 interposed therebetween such that it is magnetically coupled at a rear end portion thereof directly or by way of a non-magnetic layer to the lower layer thin film magnetic core 3, for example, through a window perforated in the insulating layers 6. Then, the thus obtained head block is polished from its front side to a location indicated by a chain line a in FIGS. 12 and 15 to form such an air bearing surface 2 as shown in FIGS. 9 and 11.
In this instance, the upper layer thin film magnetic core 4 is formed by plating a magnetic alloy such as FeNi, for example, over an entire region under the application of an external magnetic field in a predetermined direction similarly as in formation of the lower layer thin film magnetic core 3 and then etching the plated magnetic alloy film in a required pattern. Particularly, the upper layer thin film magnetic core 4 is formed in such a pattern that a narrow constricted portion 4a (FIG. 15) having a width corresponding to a required track width W.sub.T is formed at a location thereof at which a magnetic gap g is to be formed as shown in FIG. 12.
However, where the track width W.sub.T of a magneto-resistance effect type thin film magnetic head obtained in this manner is smaller than 10 .mu.m, a problem takes place that Barkhausen noises are produced significantly.
Further, a magneto-resistance effect type thin film magnetic head having such a construction as described above has another problem that such magnetic heads likely have different characteristics.
The inventors of the present invention have made various experiments and investigations and have found out that, where the lower layer thin film magnetic core 3 is formed in a magnetic core pattern of a wide area as described above, the problems arise from the fact that some disorder of magnetic domains takes place at the magneto-resistance effect magnetic sensing section 5 and upper layer thin film magnetic core 4 which are formed on such lower layer thin film magnetic core 3.
In particular, the magneto-resistance effect magnetic sensing section 5 of the magneto-resistance effect type thin film magnetic head having such construction as described above is required to be constructed such that the axis of easy magnetization thereof is directed in a track widthwise direction in order to assure a high sensitivity.
In order to direct the axis of easy magnetization of the magneto-resistance effect magnetic sensing section 5a in a track widthwise direction in this manner, such method is adopted that an external magnetic field is applied in such magnetic widthwise direction upon formation of a film of the magneto-resistance effect magnetic sensing section 5, that is, upon formation of a magneto-resistance effect thin film by vapor deposition or sputtering.
However, such external magnetic field is not very intense at the location of the magneto-resistance effect magnetic sensing section 5 because the base member 1 has a width of up to several inches. Accordingly, if the lower layer thin film magnetic core 3 of a great width is present below the magneto-resistance effect magnetic sensing section 5, then since the magnetic core 3 normally has a comparatively thick magnetic layer of several .mu.m, the magnetic field to the location of the magneto-resistance effect thin film 5 is influenced and disordered by some absorption of the magnetic field by the lower layer thin film magnetic core 3. Consequently, magnetic domains of the magneto-resistance effect thin film present such an unstable, disordered condition wherein they are inclined relative to the track widthwise direction as seen in FIG. 15.
Further, where the lower layer thin film magnetic core 3 has a great width as described hereinabove, when the upper layer thin film magnetic core 4 is to be formed similarly on the lower layer thin film magnetic core 4, even if plating of a magnetic material is performed under the application of an external magnetic field, the magnetic field is similarly influenced significantly by the lower layer thin film magnetic core 3. Consequently, magnetic domains particularly at the constricted portion 4a of the upper layer thin film magnetic core 4 to form the magnetic gap g are not arranged in the track widthwise direction, but a magnetized condition in a depthwise direction of the magnetic gap takes place dominantly. Thus, it has been found out that Barkhausen noises are caused by such magnetized condition.
Further, where the track width W.sub.T is to be defined by the upper layer thin film magnetic core 4, it is necessary for the pattern of the upper layer thin film magnetic core 4 to be formed with reference to the location of the magneto-resistance effect thin film 3 formed as a lower layer. However, it has been found out that accurate setting of the upper layer thin film magnetic core at a predetermined position relative to the magneto-resistance effect magnetic sensing section in a condition wherein a biasing conductor or a head winding is formed and consequently the distance of the upper layer thin film magnetic core 4 from the magneto-resistance effect thin film is substantially increased will actually cause a deterioration in accuracy, which will cause a dispersion in characteristic among magneto-resistance effect type thin film magnetic heads.